At present, many aircraft are equipped with Enhanced Ground Proximity Warning Systems (EGPWS), such as the system taught in U.S. Pat. No. 5,839,080, titled “Terrain Awareness System,” issued Nov. 17, 1998 to Muller et al., and herein incorporated by reference. The EGPWS combines a worldwide digital terrain database with a long-range navigation system such as Global Positioning System, INS (Inertial Navigation System), radio-dependant navigational systems, or a combination of the above. On-board computers can compare its current location with a database of the Earth's terrain. Pilots receive timely cautions and warnings of any obstructions to the aircraft's path. The EGPWS uses the intended flight path and projects a volume (or envelope) around the flight path. The volume is determined by the flight path, the aircraft capabilities, and a “buffer” zone of safety to allow for human and mechanical errors. If the projected volume intersects with terrain features or other obstacles, the EGPWS notifies the pilot.
Required Navigational Performance (RNP) is a statement of the navigation performance accuracy necessary for operation within a defined airspace. RNP extends the capabilities of modern airplane navigation systems by providing real-time estimates of navigation uncertainty, assurance of performance through its containment concepts, and features that ensure the repeatability and predictability of airplane navigation. This precise characterization of airplane performance is key to designing more efficient airspace routes and procedures. Additional information may be found in Federal Aviation Administration (FAA) Order 8400.33, Procedures for Obtaining Authorization for RNP-4 Oceanic and Remote Area Operations, and FAA Notice N 8000 RNP-SAAAR, Airworthiness and Operational Approval for Special Required Navigation Performance (RNP) Procedures with Special Aircraft and Aircrew Authorization Required (SAAAR).
RNP allows smaller, more precise flight paths than current practices, and thus may help increase the amount of air traffic allowable in an area at any given time. RNP flight paths (or RNP envelopes) are not aircraft-dependent, and are fixed in space, as opposed to the EGPWS envelopes, which are based from the aircraft. This may cause the EGPWS to trigger terrain avoidance alerts (caution or warning) because terrain or other obstacles impinges on the EGPWS alert envelope. The RNP envelope, being smaller than the EGPWS envelope, may not be impinged by the obstacle and thus, even though a terrain avoidance alert has been signaled, the aircraft may not be in a dangerous situation. In such a situation the EGPWS alert is considered a “nuisance” alert. These nuisance alerts may reduce pilot responsiveness to the EGPWS alerts; that is, the pilot may start to ignore the EGPWS alert. Additionally, the approach path designer must tailor the approach to avoid ground proximity alarms which leads to non-optimum approach paths, and sometimes the alarm conditions may not be avoidable at all.
What is needed are systems and methods of reducing the number of nuisance alerts received by a pilot.